Test-forms are evaluated one at a time in the order in which
they are given in the argument list until a test-form is found that
evaluates to true.

If there are no forms in that clause, the primary value
of the test-form is returned by the condform.
Otherwise, the forms associated with this test-form are
evaluated in order, left to right, as an implicit progn, and the
values returned by the last form
are returned by the condform.

Once one test-form has yieldedtrue,
no additional test-forms are evaluated.
If no test-formyieldstrue, nil is returned.